Identification of stereoisomers based on dielectric studies: dipole moments of chloroalkenes and chlorocumulenes

The use of dielec. measurements to assign mol. configurations was examd. with model compds. of the chloroalkane, chloroalkene and chlorocumulene type. A dielec. microcell is described which allowed measurements of 0.35 mL samples under exclusion of air. Both benzene and cyclohexane were used as solvents. Different theories of dielec. const. are compared to evaluate dipole moments. Dipole moments are analyzed in terms of bond moments. The results can be summarized as follows: (i) dielec. measurements are feasible up to 1 M solns. without substantial deviation from linearity; (ii) in general, the dipole moments found in both solvents are similar; the arom. solvent, however, causes a substantial decrease of the values obtained for chloroalkenes with two bulky substituents at the double bonds; (iii) the (E) isomers of chloroalkenes exhibit significantly higher dipole moments than the corresponding (Z) isomers; (iv) isomers of nonchlorinated alkenes of cumulenes with dipole moments below 0.6 D cannot be discriminated dielec.; (v) on the other hand, if the dipole moments of the compds. exceed 1 D, configurations can be assigned unambiguously on the basis of dielec. data even in cases where other approaches fail. [on SciFinder (R)]